Extinguishing light metal fires



rosive vapors.

. ture,

Patented Apr. 11, 1944 Richard I. Thrune, .Midland, Micln,

The DowChemical Company, Midland,

corporation of Michigan Application February '7, 1942, Serial No.429,959

No Drawing.

7 Claims.

than useless with such fires, since they are reactive chemically withthe heated metal and freassignoi' to Mich, a

quently actually accelerate the combustion.

Likewise, many common solid extinguishers are either dangerous to usewith any but small metal fires or are relatively ineffective unlessapplied in enormous quantities. Certain proprietary extinguishers areavailable, but they are usually quite expensive, and in most casesliberate during use a considerable volume of choking or cor- So far asis known, no fully sat isi'actory extinguisher has heretofore been developed. It is, therefore, an object of the present invention to providea composition and method for extinguishing light metal fires, which isnonhazardous, effective, inexpensive, and easy to ap- This object isattained in the compositions of the invention which consist essentiallyof granular carbon, e. g., ground graphite, together with from about 0.5to about 3 per cent by weight thereof of an at least semi-liquid highflash point organic substance unreactive chemically with the burningmetal, such as a heavy mineral oil. In extinguishing a light metal fire,the mixture is applied to the burning metal, whereupon the graphite inthemixture covers the hot metal so'as to exclude air therefrom and alsoconducts away the heat so rapidly that the temperature of the metal issoon reduced'to below the ignition temperature. The small proportion ofheavy oil or like substance evaporates slowly from the mixfilling theinterstices between the graphite particles with rising vapor, andthereby displacing air already present and preventing additional airfrom reaching the hot metal through the graphite. i

The carbon in the extinguishing mixture may be present as any materialwhich is composed principally of carbon and is substantially free ofvolatile materials, e. g., coke breeze, charcoal, or amorphous carbonpowder. However, graphite, usually as ground graphitized foundry coke,is greatly to be preferred in the composition both because of its muchhigher ignition temperature and its greater thermal conductivity. Thecarbon or graphite is ordinarily employed in granular form, and shouldpreferably be sufilciently fine that the final mixture is free-flowing,and yet not so fine that packing or caking occurs. Optimum results areobtained with graded graphite powder which is all finer than 8 mesh(Tyler Standard screen scale), but at least 50 per cent of which iscoarser than 200 mesh.

The minor constituent of the new composition may be any organicsubstance which has a high flash point and high boiling point, is atleast semi-liquid at room temperature, and is substantially unreactivechemically with the burning metal to be extinguished. In general, 'oilshaving a flash point above 300 F. are preferred, especially the heavyhydrocarbon or mineral oils. However, various other high flash pointoils including vegetable oils, such as cottonseed oil, synthetic oilysubstances such as diphenyl oxide, and heavy liquids or semi-solids suchas glycerine or low melting point coal-tar pitches, may also be used. ,7

In the composition of the invention, the high flash point organic liquidor semi-liquid should be present in a proportion between about 0.5 andabout 3 per cent by. weight of the granular car'- bon. With proportionsmuch below 0.5 per cent, the efiectiveness of the compositionisimpaired, whereas at percentages of liquid much above 3 percent theadvantages of the invention are not I pile of burning magnesium ormagnesium-base alloy turnings or an incendiary bomb, the composition lsmerely sprinkled over the fire with a shovel so as to cover ituniformly. The heat of the fire is conducted away rapidly and air isexeluded from the hot mass so that the blaze is quenched in a very shorttime. 1 The. quantity of the extinguishing composition necessary for anygiven fire depends, of course, upon the size and shape of the burningmaterial. In general, however, there is required roughtly one-third toan 2 i edual amount of extinguisher by weight relative to the weight ofthe hot metal. The following example will illustrate the'invention:

Example number of advantages which are not shared by other light metalfire extinguishers. The ingredients are cheap and easily compounded.'The mixture is light in weight, stable, does not tend to absorbmoisture from humid atmospheres, and remains free-flowing even afterprolonged storage in open air. It is non-abrasive and nonreactivechemically with hot metal. Unburned portions of the metal are notdestroyed or coated with residues which are difficult to remove, but

can be recovered very readily. The extinguisher gives off little if anyfumes and no corrosive vapors.

Because of the oil content, the composition is virtually non-dusting,even when sprinkled; yet the oil, being present only on the surface ofthe graphite particles, does not tend to run out of the composition onstanding. When the extinguisher is applied to a metal fire, the heavyoil, as explained, evaporates slowly, the vapors so formed filling thespace between graphite particles and excluding air from the fire.However, theseva- DOlS are present in such small amount that, althoughthey are flammable, they do not form a sustained flame over the surfaceof the extinguisher which has been applied to the metal fire. A fewscattered flashes may occur momentarily, but there are no continuousheat-producing flames which must be extinguished. As a result,

the application of the new composition does not give rise to secondaryfires which sometimes reignite the light metal while it is stil1 hot andwhich always require attention in main metal fire.

addition to the Extra point above about 300 F.

This application is a continuation-in-part of prior application SerialNo. 364,493, filed Novemher 6, 1940.

What is claimed is: a

1. A composition for extinguishing light metal fires-which consistsessentially of an intimate mixture of granular carbon together with from0.5 to about 3 per cent by weight thereof of an at least semi-liquidhigh flash point organic substance unreactive chemically with theburning metal.

2. A composition according to claim l wherein the carbon is present inthe form of graphite.

3. A composition according to claim 1 wherein the organic substance isan oil having a flash 4. A free-flowing substantially non-dustingcomposition for extinguishing light metal fires which consistsessentially of granular graphite, the particles of which are coated witha mineral oil having a flash point above about 300 F., the oil beingpresent in a proportion from between about 0.5 to about 3 per cent byweight of the graphite.

5. A composition according to claim 4 wherein the granular graphite ispresent as graded powder in which all the material has substantially aparticle size-finer than 8 mesh and at least 50 per cent of suchmaterial is coarser than 200 mesh.

6. A method of extinguishinga light metal fire which comprises applyingto the burning metal a composition consisting essentially of an intimatemixture of granular carbon together with from about 0.5 to about 3 percent by weight thereof of an at least semi-liquid high flash pointorganic substance unreactive chemically with the burning metal.

7. A method of extinguishing magnesium and magnesium alloy fires whichcomprises applying to the burningmetal in a quantity sufficient toextinguish the fire a composition consisting essentially of granulargraphite, the particles of which are coated with a mineral oil having aflash point above about 300 F., the oil being present in a proportionfrom between about 0.5 to about 3 per cent by weight of the graphite.

' RICHARD L THRUNE.

